(Nature) Quantum key distribution has reached the level of maturity required for deployment in real-world scenarios. It has previously been shown to operate alongside classical communication in the same telecommunication fibre and over long distances in fiber and in free-space links. Despite these advances, the practical applicability of quantum key distribution has been curtailed until now by the fact that most implementations and protocols are limited to two communicating parties.
Recently, a team of researchers from Austria announced their approach which offers scalability to a large number of users. Sören Wengerowsky, Siddarth Koduru Joshi, Fabian Steinlechner, Hannes Hübel & Rupert Ursin published their approach using a single source of bipartite polarization entanglement, which is multiplexed into 12 wavelength channels. Because no adaptations of the entanglement source are required to add users, the network can readily be scaled to a large number of users, without requiring trust in the provider of the source. The implementation is fully passive and thus has the potential for unprecedented quantum communication speeds.